Having fallen behind to a Juan Mata strike, Swansea boss Garry Monk brought Ki Sung-yueng on for Wayne Routledge, changing the shape of his team in a bid to find an equaliser.

Two goals in the space of five minutes followed, from Andre Ayew and Bafetimbi Gomis respectively, as Swansea recorded a third-consecutive 2-1 win against the Old Trafford club.

"After 1-0 they changed the shape and then we could not cope with that, so that's not good," Van Gaal told Sky Sports. "For five minutes we lost our dominant role and that was a pity because I think we controlled the game.

"When you don't know it [the formation] then you have to be compact.

"You saw Swansea in the last 20-25 minutes, they were compact and it's always difficult to beat a compact team.

"We could have scored much more goals, so I don't think that's the problem. When you create chances that's the biggest issue, and you also need a little bit of luck."

Asked for his view on Swansea's goals, Van Gaal added: "When the opponent scores a goal you can always find errors but I have to analyse that with my players."